The purpose of this study is to identify patients whose hypertension is caused by inappropriate secretion of adrenal steroid (usually aldosterone), and to separate those who are likely to benefit from surgery from others who are more suitable for medical treatment. In most cases, an aldosterone-producing adenoma (APA) responds to circadian changes in circulating ACTH, but not to other stimuli which control aldosterone secretion in normals and other hypertensive patients. We are searching for the most effective means to identify patients with APA. Tests include circadian rhythms (spontaneous and modified by posture or drugs), administration of potential adrenal stimuli or blocking agents, venous catheterization, radiological examination and scanning. Other procedures involve measurements of aldosterone binding to plasma proteins and red blood cells, and the concomitant modification of aldosterone distribution and metabolism. In patients with no demonstrable APA, the relation between aldosteronism and hypertension is obscure, and we are seeking better understanding of the pathophysiology of hypertension, as well as improved methods of treatment.